Vacuum-type circuit interrupter



Nov. 28, 1967 J. w. RANHEIM VACUUM-TYPE CIRCUIT INTERRUPTER Filed June 5, 1966 I N V EN TOR. //z77 2M- Ran/761m fit torngr United States Patent 3,355,564 VACUUM-TYPE CIRCUIT INTERRUPTER John W. Ranheirn, 6452 s. 13th St.,

Oak Creek, Wis. 53154 Filed June 3, 1966, Ser. No. 555,079 14 Claims. (Cl. 200-444 ABSTRACT OF THE DISCLOSURE An arc interrupting device including an evacuated envelope comprising a pair of elongate, hollow, open-ended insulating members joined by means of a butt seal to an open-ended arcing chamber having a bulbous center portion and a bulbous arc shield afiixed to the arcing chamber and extending toward the opposite ends of the housing. The are shield is characterized by a high thermal conductivity, and the arc chamber is characterized by high strength and a thermal coeflicient of expansion substantially closer to that of the housing portions than that of the arc shield.

Cross reference to related application This is a continuation-in-part of copending application Ser. No. 380,193, now abandoned, filed July 3, 1964.

Background of the invention The invention relates to circuit interrupters and, more particularly, to new and improved vacuum-type circuit interrupters.

When current is interrupted in a vacuum-type circuit interrupter, an arc is initiated by electrons emitted from the surface of one of the spaced electrodes thereof, which instantaneously acts as a cathode, and flows to the other electrode, which instantaneously acts as an anode. In addition, the arc liberates gases from the surface of the electrodes and vaporizes a small portion of the metallic electrode material and these particles become ionized to help sustain the arc. It has been found that by moving the arc rapidly along the surface of the electrodes, are interruption is facilitated because lower contact temperature is achieved to reduce thermal electron emission and, further, because there is a reduction in the quantity of electrode material vaporized and a greater dispersion of the electrode material that is vaporized to provide faster dielectric recovery in the electrode gap.

One prior art method for moving the arc in vacuumtype interrupters is to provide an enlarge electrode arcing region and current-carrying means for establishing a magnetic field which moves thearc rapidly about the contacts outer periphery. These electrode arcing regions take the form of helically slotted disc-like members which provide a generally spiral current path.

The vacuum envelope of most prior art volume circuit interrupters includes a hollow cylindrical housing of insulating material, such as glass, and a pair of sealing metallic end caps. In order to prevent vaporized electrode material, incident to an arc interruption, from condensing on the relatively cool inner surface of the insulating housing, and thereby to provide a shunt current path around the electrodes, an arc shield generally separates the electrodes from the inner surface of the insulating housing.

As a result of this disc-like electrode configuration and of the requirement for an arc shield, the insulating housings of prior art vacuum interrupters had relatively large diameters. Such insulating housings were costly due to the difliculties involved in fabricating large glass housings and in sealing such housings to the metallic caps which close their ends.

One prior art vacuum interrupter attempted to solve this problem by providing a pair of tubular insulating housing portions joined by a bulbous arcing chamber having a substantially larger diameter than the housing portions. This arcing chamber provided a condensing surface for vaporized contact material and acted to absorb arc energy, necessitating the use of a high thermal conductivity material, such as copper. Because of the strength characteristics of such high thermal conductivity metals, these arcing chambers had to be relatively thick in order to withstand the pressure differential between the vacuum on its inner surface and the atmosphere on its exterior. Thick arcing chambers of this type were relatively diflicult to seal to the ceramic or glass housing portions because of the large diiference in their thermal coefiicients of expansion. As a result, it was necesesary to provide a relatively thin transition member therebetween so that it would more easily conform to the differently expanding ceramic housing portions. This tended to increase the cost of the seal even though it is physically Weak.

The steady state pressure within most prior art vacuum interrupters is in the order of 10* to 10* mm. Hg. However, during an arc interruption, the release of surface gases, even from clean electrodes, causes the pressure to rise to the order of 10* to 10- mm. Hg. While this increase in pressure is only temporary, as the result of the gettering action of the vaporized contact material which condenses on the inner surfaces of the interrupter, it momentarily causes a substantial reduction in the interrupters breakdown voltage. As a result of this pressure increase, some prior art vacuum interrupters were prone to restrike after an arc interruption.

Such restriking is believed to be caused by the avalanche multiplication of electrons resulting from the ionization of gas molecules struck by emitted electrons. This occurs where the electron mean free path in the interrupter is less than the straight line distance that an electron must travel in going from anode to cathode potential. The electron mean free path is, of course, the distance an electron must travel between collisions with gas molecules and is a function of the gas pressure.

Because at normal vacuum interrupter pressures the electron mean free path is in the order of 5 l0 to 5 10 cm., ar-over as the result of emitted electrons is generally not a problem. However, because the mean free path reduces to 5-10 cm., as the result of the pressure rise incident to an arc interruption, many prior art interrupters are vulnerable to restrike. This is believed to be a particular problem in interrupters wherein there are relatively large straight line paths between spaced points having large potential diiferences.

It is an object of the invention to provide a new and improved vacuum circuit interrupter.

A further object of the invention is to provide a vacuum circuit interrupter having a pair of insulating housing portions and a relatively strong, thin metallic arcing chamber wherein a relatively thin high thermal conductively arc shield is interposed between the arc chamber and interrupting contacts.

Yet another object of the invention is to provide a vacuum circuit interrupter having arc shields which closely surround the arcing contacts.

Another object of the invention is to provide a vacuum circuit interrupter having a pair of insulating housing portions and a central arcing chamber joining the housing portions and an arc shield interposed between arcing contacts and the arcing chamber, wherein the coefficient of expansion of the arc shield is substantially closer to that of the housing portions than is that of the arc shield.

Still another object of the invention is to provide a A further object of the invention is to provide a vacuum circuit interrupter wherein the distance between its arc shield and arcing contacts is substantially smaller than the electron mean free path therein during an are interruption.

Another object of the invention is to provide a vacuum circuit interrupter whose arcing contacts and arc shield are so configured that particles liberated during arcing are confined to the arcing chamber and which eliminate all long line-of-sight paths between spaced points carrying full interrupter voltage.

Brief description of the drawings FIG. 1 is a side elevational view, partly in section, of a vacuum-type circuit interrupter according to the instant invention;

FIG. 2 is a fragmentary view of the interrupter shown in FIG. 1; and

FIG. 3 is a view taken along lines 3-3 of FIG. 1.

Description of the preferred embodiment Referring now to the drawing in greater detail, FIG. 1 shows the vacuum-type circuit interrupter according to the instant invention as having an outer sealed envelope designated by the general reference numeral 10, a fixed contact rod or electrode 11 and a movable contact rod .or electrode 12. The contact rods 11 and 12 are coaxially aligned within the envelope 11 and respectively carry arcing regions or contacts 13 and 14 at their inner ends. Means, not shown, but which are well known in the art, are provided for moving the contact rod 12 between its closed positions shown by phantom lines in FIG. 1 to its open positions shown by full lines.

The envelope includes a pair of hollow, elongate, tubular, open-ended housing portions 16 and 17, which may be composed of any suitable insulating material, such as ceramic. The insulating housing portions 16- and 17 are arranged in axially aligned spaced relation relative to each other and are coaxial with the contact rods 11 and 12, respectively.

The envelope 10 also includes a bulbous arcing chamber 18 disposed between the insulating housing portions 16 and 17 and formed by a pair of metallic bell-shaped members 20 and 21. The members 20 and 21 each have a small diameter throat portion 22 at one end and flare outwardly therefrom to a large-diameter mouth portion 23 at the opposite end. The opening in each throat portion 22 abuts the end of its associated insulating housing portion 16 or 17 and each is suitably affixed thereto to form a butt seal. The members 20 and 21 are provided with opposed flanges 24 which extend outwardly from the periphery of each month portion 23 and which are attached in any suitable manner such as by welding.

The butt joint between the ceramic housing portions 16 and 17 and the various metallic portions of the envelope is shown in greater detail in FIG. 2. The end face of the housing portion 17 is first ground flat and then a suitable metallic coating 25, such as an alloy of 85% Mo and 15% Mn, is applied in a manner well known in the art. A nickel plating 29 is applied to the coating 25 and the metal portion 22 is then brazed thereto. This provides a joint which is stronger than the ceramic itself and does not require a reduction in thickness of the metallic portions of the envelope 10.

The arcing contacts 1 3 and 14 are generally discshaped and are disposed in an opposed relation relative to each other. Because of the bulbous central portion of the arcing chamber 20, the diameter of the contacts 13 and 14 may be larger than the inside diameter of the housing portions 16- and 17.

The opposite ends of the envelope 10 are closed by a pair of closure caps 26 and 27, each of which has a peripheral flange which is suitably affixed in a sealing relation to the outer ends of the insulating housing portions 16 and 17, respectively. The closure cap 26 has a central opening 29 which is suitably afiixed to the stationary contact rod 11 to seal the stationary contact end of the envelope 10. The other end cap 27 also has a central opening 30 which is spaced from the movable contact rod 12 and which is sealed by a bellows 32 aflixed at one end to the end cap 27 around the opening 30 and at its other end to a cap 34 affixed intermediate the ends of movable contact rod 1 2. The cap 34 has a skirt portion 35 extending toward the closure cap 27 and serves the purpose of electrostatically shielding the juncture between the end cap 27 and the ceramic housing portion 17. A similar cap 3-6 is aflixed to the stationary contact rod 11 to provide electrostatic shielding at the opposite end of the envelope 10.

An arc shield 38 is disposed within the envelope 11 and has a bulbous central section 39 which is shaped similarly with the arcing chamber 18 and is aflixed to the inner surface thereof. In addition, the arc shield has a pair of skirt portions 40 which extend from the central section 39 toward the end caps 26 and 27 and between the contact rod and the housing portion on each side of the envelope 1%. The are shield 33 serves the purpose of confining the arcing products, absorbing arc energy and preventing vaporized contact material form condensing along the inner surfaces of the insulating housing portions 16 and 17 and thereby creating a shunt current path around the interrupting contacts 13 and 14. In addition, the skirt portions 40 electrostatically shield the joints between the arcing chamber 18 and the housing portions 16 and 17.

As seen in FIGS. 1 and 3 the arcing contact 13 is generally disc-shaped and is afiixed in any suitable manner, such as by brazing to the lower end of the contact rod 11. In addition, the front face of the contact 13 is provided with a generally circular recess 43 to provide a generally annular contact face 44 around the central recess 43 for engagement with the contact 14 as shown in FIG. 3. As a result, the current flowing between the contact rods 11 and 12 and through the contacts 13 and 14 loops outwardly so that the resulting electromagnetic field tends to lengthen the loop and thereby to move the cur.- rent to the outer periphery of the contacts 13 and 14.

As seen in FIG. 3, a plurality of spaced, arcuate, spirally arranged slots 46 are formed in each of the con tact members 13 and 14 and extend generally outwardly from a point adjacent the recess 43 to an outer end which terminates adjacent the outer periphery of the contact member 14 and is generally tangent thereto. These arcuate slots 46 force the current flowing in the contact member 14 to follow a generally spiral path as shown by the dashed lines i in FIG. 3. This arcuate current path set up in the contact 13 provides, in effect, a coil which establishes a magnetic field in a manner well known in the art. When the circuit breaker contacts part, as illustrated by full lines in FIG. 1, the magnetic field in the area of the gap between the contacts 13 and 14 will produce a force acting on the arc and tending to move it rapidly around the outer peripheries of the contacts 13 and 14. For a more complete description of the contacts 13 and 14, reference is made to copending application Ser. No. 380,192, filed July 3, 1964 and assigned to the assignee of the instant invention.

A generally frustoconical arc shield 48 is affixed to the back of each of the contacts 13 and 14 to prevent vaporized contact material from passing through the slots 46 to the upper and lower ends of the envelope 10. The arc shield 48, which may be of a ferromagnetic material, can also provide a magnetic circuit path for the flux which is generated by the current in the contacts 13 and 14. The contacts 13 and 14 are composed of a conductive non-magnetic material such as copper or an alloy thereof, which has a much higher conductivity than that of the shield 48, so substantially no current fiows in said shield to bypass the contacts.

The vacuum interrupter envelope 10, according to the instant invention, allows the use of large diameter slotted disc-shaped arcing contacts 13 and 14 without suifering the disadvantage of requiring a'relatively large and expensive glass insulating housing. By employing an envelope having a pair of tubular insulating housing portions and a bulbous arcing chamber therebetween, each of the insulating housing portions may have a relatively small diameter, which is just large enough to accommodate the contact rods 11 and 12 and the arc shield 38 disposed therearound. The small diameter of the insulating housing portions 16 and 17 is also possible because of the bulbous shapes of the arcing chamber 18 and the arc shield 38 whereby the skirt portions 40 of the arc shield 38 have a smaller diameter than that of the arcing contacts 13 and 14. The small diameter housing portions 16 and 17 are less expensive to fabricate than a single large diameter member and, in addition, their smaller diameters are easier to seal to the metallic end caps 26 and 27.

It can be seen that the arc shield 38 is configured to generally conform to the shape of the arcing contacts 13 and 14 and is disposed in close proximity thereto. In fact, the distance between the contacts and the arc shields are approximately the same as the distance between the contacts themselves. This distance is a fraction of the electron mean free path at pressures which occur within the interrupter during arcing. For example, in one embodiment of the invention, the maximum distance between the contacts 13, 14 and the are shield 38 is in the order of two cm., while the electron mean free path during arcing is in the order of 5-10 cm. i

In addition, the configuration of the contact shield acts to confine vaporized contact material and gases liberated during arcing to the space surrounding the electrodes. This tends to limit the incidence of ionized particles in the end areas of the interrupter wherein longer distances exist between points at different electrical potentials. Also the configuration and location of the shields 35, 36 and 48 divide the long line-of-sight paths along the length of the interrupter.

Preferably the arc shield 38 is composed of a material which has a high thermal conductivity for absorbing are energy. The chamber 18, on the other hand, must be sufficiently strong to withstand the pressure drop across it, must be corrosion resistant, and should 'be readily joinable with the insulating housing portions 16 and 17. By providing two distinct members for the arcing chamber 18 and the arc shield 38, the desirable, and yet distinct properties of each can be achieved. For example, the arc shield 38 may be composed of a high thermal conductivity metal such as copper. The arcing chamber 38 may be composed, for example, of Kovar which is highly corrosion resistant and sufficiently strong so that a relatively thin section can withstand the pressure drop. In addition the thermal coefficient of expansion of Kovar is sufiiciently similar to that of the ceramic housing portions 16 and 17 to allow an inexpensive direct seal, such as the butt seal shown in FIG. 2. This eliminates the necessity for a costly thinned transition section at the seal as required in prior art interrupters.

In one example of an interrupter made according to the instant invention, the ceramic housing portions 16 and 17 are composed of ceramic No. 4462 of the Frenchtown Porcelain Co. of Frenchtown, N.J., which is 94% A1 0 and which has a coefficient of linear expansion of 7.29 C. at 30600 C.; the arcing chamber is composed of Kovar, an alloy, having 29% Ni, 17% Co and the balance FE and which has a coefiicient of linear expansion of 7.29X10 C. at 25-700" 0.; and the arcing shield is substantially pure copper whose coeflicient of linear expansion is 16.07X1O C. at 0-6250 C.

While the invention has been described and illustrated with respect to a particular vacuum interrupter, those skilled in the art will understand that deviations in the design are possible without deviating from the spirit of the invention. In addition, while the interrupter has been described with respect to particular materials and a particular contact configuration, these are merely intended as examples. Accordingly it is not intended to limit the invention to the foregoing description but only by the scope of the appended claims.

Iclaim:

1. An are interrupting device including an evacuated envelope, said envelope including a pair of elongated hollow open-ended insulated housing portions, a hollow open-ended arcing chamber composed of relatively thin metallic material and being disposed between said insulating housing portions, first sealing means for affixing said chamber toone end of each of said housing portions, means for sealing the other ends of each of said insulating housing portions, a pair of electrodes disposed within said envelope, an enlarged arcing region provided on each of said electrodes, said arcing regions being disposed in an opposed relation within said arcing chamber and each having a transverse dimension which is large relative to the diameter of said housing portions, said arcing chamber having a central portion whose transverse dimension is substantially larger than that of said housing portions and whose axial length is substantially shorter than that of said insulating housing portions, and a thin-walled metallic arc shield disposed between said arcing regions and said arcing chamber and having a bulbous central portion afiixed to said arcing chamber and end portions extending therefrom toward the other ends of said housing portions and between said housing portions and said electrodes, said end portions also being disposed between said electrodes and said first sealing means, said are shield being composed of a first metallic material characterized by a high thermal conductivity and said arcing chamber being composed of a different metallic material characterized by a substantially greater ability to resist deformation as a result of a large pressure differential across it than is said are shield.

2. The arc interrupter set forth in claim 1 wherein the metal of said arcing chamber is characterized by a thermal coefiicient of expansion which is substantially closer to that of said housing portions than is that of said arc shield.

3. The are interrupter set forth in claim 1 wherein said arcing chamber is joined directly to said insulating housing portions without any substanial reduction in thickness.

4. The are interrupter set forth in claim 1 wherein the distance between said are shield and said electrodes is substantially smaller than the electron means free path within said interrupter during an arc interruption.

5. The are interrupter set forth in claim 1 wherein said housing portions are generally tubular and said electrodes comprise a stationary and a movable electrode each extending generally axially through one of said housing portions and wherein said arcing regions are generally discshaped contacts, the end portions of said are shield being substantially smaller than that of said central portion to substantially confine the vaporized contact materials and gases liberated during an arc interruption, said are shield and said contacts cooperating to eliminate any long lineof-sight paths between spaced points carrying the full interrupter voltage.

6. The are interrupter set forth in claim 1 wherein the ends of said arcing chamber is afiixed in an abutting relation to the said one ends of said housing portions to pro vide said first sealing means.

7. The are interrupter set forth in claim 3 wherein the distance between said are shield and said electrodes is substantially smaller than the electron means free path within said interrupter during an arc interruption.

8. The are interrupter set forth in claim 3 wherein the ends of said arcing chamber is affixed in an abutting relation to the said one ends of said housing portions to provide said first sealing means.

9. The are interrupter set forth in claim 4 wherein said housing portions are generally tubular and said electrodes comprise a stationary and a movable electrode each extending generally axially through one of said housing portions and wherein said arcing regions are generally disc-shaped contacts, the end portions of said are shield being substantially smaller than that of said central portion to substantially confine the vaporized contact materials and gases liberated during an arc interuption, said are shield and said contacts cooperating to eliminate any long line-of-sight paths between spaced points carrying the full interrupter voltage.

10. The arc interrupter set forth in claim 7 wherein said housing portions are generally tubular and said electrodes comprise a stationary and a movable electrode each extending generally axially through one of said housing portions and wherein said arcing regions are generally disc-shaped contacts, the end portions of said are shield being substantially smaller than that of said central portion to substantially confine the vaporized contact materials and gases liberated during an arc interruption, said are shield and said contacts cooperating to eliminate any long line-of-sight paths between spaced points carrying the full interrupter voltage.

11. The are interrupter set forth in claim 3 wherein the distance between said are shield and said electrodes is substantially smaller than the electron means free path within said interrupter during an arc interruption.

12. The are interrupter set forth in claim 11 wherein said arcing chamber is joined directly to said insulating housing portions without any substantial reduction thickness.

generally disc-shaped contacts, the end portions of said arc shield being substantially smaller than that of said central portion to substantially confine the vaporized contact materials and gases liberated during an arc interruption, said are shield and said contacts cooperating to eliminate any long line-of-sight paths between spaced points carrying the full interrupter voltage.

References Cited UNITED STATES PATENTS 3,082,307 3/1963 Greenwood etal. 200-44 3,141,058 7/1964 Titus 200 144 3,163,734 12/1964 Lee 1, 200-144 3,187,083 6/1965 Grimes.

3,231,704 1/1966 Jacobs 200-144 3,280,286 10/1966 Ranheim 200-144 FOREIGN PATENTS 153,318 5/1963 Russia.

ROBERT S. MACON, Primary Examiner. 

1. AN ARCH INTERRUPTING DEVICE INCLUDING AN EVACUATED ENVELOPE, SAID ENVELOPE INCLUDING A PAIR OF ELONGATED HOLLOW OPEN-ENDED INSULATED HOUSING PORTIONS, A HOLLOW OPEN-ENDED ARCING CHAMBER COMPOSED OF RELATIVELY THIN METALLIC MATERIAL AND BEING DISPOSED BETWEEN SAID INSULATING HOUSING PORTIONS, FIRST SEALING MEANS FOR AFFIXING SAID CHAMBER TO ONE END OF EACH OF SAID HOUSING PORTIONS, MEANS FOR SEALING THE OTHER ENDS OF EACH OF SAID INSULATING HOUSING PORTIONS, A PAIR OF ELECTRODES DISPOSED WITHIN SAID ENVELOPE, AN ENLARGED ARCING REGION PROVIDED ON EACH OF SAID ELECTRODES, SAID ARCING REGIONS BEING DISPOSED IN IN AN OPPOSED RELATION WITHIN SAID ARCING CHAMBER AND EACH HAVING A TRANSVERSE DIMENSION WHICH IS LARGE RELATIVE TO THE DIAMETER OF SAID HOUSING PORTIONS, SAID ARCING CHAMBER HAVING A CENTRAL PORTION WHOSE TRANSVERSE DIMENSION IS SUBSTANTIALLY LARGER THAN THAT OF SAID HOUSING PORTIONS AND WHOSE AXIAL LENGTH IS SUBSTANTIALLY SHORTER THAN THAT OF SAID INSULATING HOUSING PORTIONS, AND A THIN-WALLED METALLIC ARC SHIELD DISPOSED BETWEEN SAID ARCING REGIONS AND SAID ARCING CHAMBER AND HAVING A BULBOUS CENTRAL PORTION AFFIXED TO SAID ARCING CHAMBER AND END PORTIONS EXTENDING THEREFROM TOWARD THE OTHER ENDS OF SAID HOUSING PORTIONS AND BETWEEN SAID HOUSING PORTIONS, AND SAID ELECTRODES, SAID END PORTIONS ALSO BEING DISPOSED BETWEEN SAID ELECTRODES AND SAID FIRST SEALING MEANS, SAID ARCH SHIELD BEING COMPOSED OF A FIRST METALLIC MATERIAL CHARACTERIZED BY A HIGH TERMAL CONDUCTIVITY AND SAID ARCING CHAMBER BEING COMPOSED OF A DIFFERENT METALLIC MATERIAL CHARACTERIZED BY A SUBSTANTIALLY GREATER ABILITY TO RESIST DEFORMATION A RESULT OF A LARGE PRESSURE DIFFERENTIAL ACROSS IT THAN IS SAID ARC SHIELD. 